Dipped headlights for motor vehicles conventionally consist of a reflecting mirror sending light rays emitted by a light source towards the front of a vehicle and a glass possibly altering the path of these rays, in order to obtain a light beam having a predetermined photometry.
In a known manner, it is necessary to use a reflecting mirror of relatively large dimensions, particularly in width, in order to obtain a dipped headlight which complies both with the regulations in force and which is of high performance.
These large dimensions of the reflecting mirror are necessary in order, on the one hand, to recover a sufficient amount of the light flux emitted by the source and, on the other hand, to generate, in some regions of the mirror, images of the source which are small enough to form, in the dipped beam, a spot the concentration of which is intense enough to improve the range of the headlight.
Conventionally, the larger the mirror, for a given basic focal length, the larger the solid angle covered by the mirror seen by the source, and therefore the better the rate of recovery of the light flux coming from the source. However, the two objectives mentioned above are contradictory: the smaller the basic focal length of the mirror, that is to say the more the mirror is closed around the source, for a given height and width, the better the flux recovery, but the images of the source are all enlarged, and the range is insufficient. In contrast, if a longer basic focal length is used, the range is improved but the overall intensity of the beam is decreased in an undesirable manner.
This then results in the provision of mirrors comprising regions with different focal lengths, so as to improve both the range and the intensity of the beam, by combining the advantages of regions with short and with long focal lengths. The surface of mirrors designed in this way then has discontinuities and steps, which make the manufacture of such mirrors, their metallization and their final laquering difficult.